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Elective Surgery is Essential - August 2020 - Subscribe to Outpatient Surgery Magazine

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MYTH #3: MH does not occur after administration of succinylcholine alone FACT: Most MH cases are associated with the admin- istration of a volatile anesthetic gas with or without succinylcholine. Many anesthesia providers are under the impression that because the use of suc- cinylcholine is so common — and MH is so unusual — that the two are not related. Although rare, we are aware of cases of proven MH that occurred after administration of succinylcholine alone. However, unlike Myth #2, the clinical syndrome usually mani- fests as marked muscle rigidity (generalized or con- fined to the masseter muscles), respiratory and meta- bolic acidosis, rhabdomyolysis and high temperature. MYTH #4: Patients with a family history of MH are susceptible only if MH occurred in a first-degree relative FACT: I recently took care of a child whose moth- er's great uncle had proven MH susceptibility. Some anesthesia providers believe that since no one else in the family between these generations developed MH, then the child has the same risk of MH as the general population. Although a classic Mendelian inheritance of MH is an oversimplification, MH sus- ceptibility is inherited in an autosomal dominant pattern. This means that having a mutation in only one copy of the responsible gene (one parent) is enough to confer MH suscepti- bility. With every generation, the risk of MH susceptibility decreases by 50%. Using a con- servatively high prevalence of MH variants of approximately 1 in 1,500 in the general popula- tion, it would take approxi- mately 10 generations to decrease the calculated familial risk to be similar to that of the general population. As this example illustrates, any familial history within 10 generations (essentially everyone) should be cause for suspicion of MH susceptibility. In my patient's case, the causative variant may have started five generations away, which puts the child's risk at about 3%, still much higher than the general population. Therefore, the child should receive MH precautions, meaning anesthesia with non-triggering agents. MYTH #5: MH occurs mainly in children FACT: Because MH is a genetic disorder, its sus- ceptibility has nothing to do with age. It may mani- fest itself earlier when children have surgeries, but epidemiologic studies demonstrate that the medi- an age of an acute MH reaction is about 19 years. This means that about half of all MH reactions occur in children and half occur in adults. While we're on the subject, a previous safe anesthetic with triggering agents is no guarantee that MH won't occur again in that patient when triggering anesthetics are administered. Approximately half of patients who develop MH have had one or two uneventful exposures to triggering agents. In fact, MHAUS is aware of a patient with confirmed MH who had received approximately 30 anesthetics before their triggering event. MYTH #6: The MH-related mortality rate is 10% to 15% FACT: Some textbooks and database-driven studies have estimated that approximately 10% to 15% of 4 2 • O U T P A T I E N T S U R G E R Y M A G A Z I N E • A U G U S T 2 0 2 0 READY TO RESPOND Surgical teams who understand the risk factors of MH and practice response protocols are better prepared to manage a crisis.

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